What is the equivalent dose of metoprolol (beta-blocker) immediate release when converting from metoprolol extended release?

Metoprolol Extended Release to Immediate Release Dose Conversion

Direct Conversion Recommendation

When converting from metoprolol succinate extended-release (ER) to metoprolol tartrate immediate-release (IR), use the same total daily dose but divide it into twice-daily administration. 1

Conversion Algorithm

Step 1: Calculate Total Daily Dose

• Identify the current metoprolol succinate ER dose (given once daily)
• This becomes your total daily metoprolol tartrate dose 1

Step 2: Divide for Twice-Daily Dosing

• Split the total daily dose in half for administration every 12 hours 1
• Example: Metoprolol succinate ER 100 mg once daily converts to metoprolol tartrate IR 50 mg twice daily 1

Step 3: Verify Dose Ranges

• For hypertension: Metoprolol tartrate maximum is 200 mg daily (100 mg twice daily), while metoprolol succinate maximum is 400 mg daily 1, 2
• For heart failure: Metoprolol tartrate maximum is 200 mg twice daily, while metoprolol succinate target is 200 mg once daily 1, 2

Key Pharmacokinetic Differences to Understand

The formulations differ significantly in their drug delivery profiles:

• Metoprolol tartrate (IR) produces marked peaks and troughs in plasma concentrations, requiring twice-daily dosing 3
• Metoprolol succinate (ER) delivers drug at a near-constant rate over 20 hours, producing even plasma concentrations over 24 hours without significant peaks 3
• The ER formulation maintains consistent beta-1 blockade throughout the day while the IR formulation has more variable coverage 3, 4

Monitoring After Conversion

Immediate Assessment (First 24-48 Hours)

• Check heart rate and blood pressure 2-4 hours after each IR dose to capture peak effects 1
• Monitor for symptomatic bradycardia (HR <60 bpm with dizziness) 1
• Assess for hypotension (systolic BP <100 mmHg with symptoms) 1

Ongoing Monitoring (First 2 Weeks)

• Evaluate for breakthrough symptoms between doses, as IR formulation may have less consistent coverage 3, 4
• Watch for worsening heart failure symptoms if converting in HF patients 1
• Target resting heart rate of 50-60 bpm unless limiting side effects occur 1

Common Pitfalls to Avoid

• Do not use a 1:1 milligram conversion and maintain once-daily dosing - this will result in inadequate coverage for the second half of the day due to the shorter half-life of metoprolol tartrate 3, 4
• Do not split the dose unevenly - maintain equal twice-daily dosing to ensure consistent beta-blockade 1
• Never abruptly discontinue during conversion - this can precipitate severe exacerbation of angina, myocardial infarction, and ventricular arrhythmias with up to 50% mortality 1
• Do not convert in unstable patients - ensure hemodynamic stability before switching formulations, particularly in decompensated heart failure 1, 2

Special Considerations for Specific Conditions

Heart Failure Patients

• The ER formulation (metoprolol succinate) is preferred and evidence-based for heart failure with reduced ejection fraction 2, 5, 6
• If conversion to IR is necessary, use the same total daily dose divided twice daily, but recognize this is off-label for heart failure 1, 2
• Monitor closely for decompensation during the conversion period 1

Post-Myocardial Infarction

• Standard protocol uses metoprolol tartrate 50 mg every 6 hours for 48 hours initially, then transitions to twice-daily dosing 2
• Maintenance dosing is typically 100 mg twice daily 2

Hypertension and Angina

• Conversion is straightforward using the same total daily dose divided twice daily 1
• The IR formulation may require dose adjustments if blood pressure control is inadequate between doses 4